Method of preparing coated asbestos cement shingle and product thereof



3,462,237 METHUD QF PREPARENG COATED AShESTGS (IEMENT SHINGLE AND PRGDUCT THEREGF Herbert A. Marshall, Crown Point, Ind, assignor to United States Gypsum Company, Chieago, lilL, a corporation of Delaware No Drawing. Filed Apr. 15, P966, Ser. No. 542,761 Int. (Cl. 5303c 17/32; 344d 1/46 US. Cl. 11737 9 Claims ABSTRAQT 6F THE DTSCLUSURE A process for coating asbestos shingles with a discontinuous water-resistant coating is disclosed. This coating is applied to less than the entire area of the shingle of prevents warping. This discontinuous coating is applied to the back surface and then the shingle is predried at elevated temperatures. The shingle is then cooled and coated with a weather resistant coating on the other side. The weather resistant coating is applied to the whole shingle. The shingle is then baked to cure this coating and thereafter the moisture content is adjusted.

This invention relates to an improved process for preparing a coated asbestos cement shingle and to the product produced thereby and more particularly to a substantially warpfree asbestos cement shingle which has a coating upon the exterior face thereof.

Asbestos shingles, as they are known in the building trades, are conventionally formed from a mixture of portland cement, asbestos fibers and finely divided silica flour by a wet process on the well-known Hatschek machine. These sheets are often formed with a plurality of grooves, simulated striations or score marks on one surface (to give the visual impression of split cedar shakes) of elongated sheets with the grooves running parallel to the short dimension of sheets about 2 /2 or 3 feet by 1 foot. The surface, scored or smooth, is often coated with a baked-on finish. The process steps include forming the shingle from the mix, curing, predrying to reduce moisture to about 2% or less, cooling and applying a weather resistant coating to the exterior or weather surface, baking the shingle to dry the coating, and further reducing the moisture content to less than about 1% moisture content followed by water spraying which raises the moisture content to about 4%, which is approximately that reached under ordinary job conditions.

Asbestos cement shingles manufactured by the techniques described above have a tendency to warp when the exterior finish or weather surface is coated with a bakedon finish and/ or embossed so as to impart certain aesthetic values thereto. In some cases the warping has been so severe as to interfere with the proper application of the shingle. The warping is especially severe when fairly deep closely spaced grooves are embossed into the exterior or weather surface parallel to the short side of the shingle and the embossed surface is further covered with a baked-on coating. The warping consists of a slight arcuate bend or bow in the body of the shingle such that it tends to form a segment of a cylindrical surface with a very long radius and having an axis parallel to the short edges. The face is usually warped convex. The warp most noticeably takes place in shingles of short lengths, such as those of about 27". Shingles of about a 48" length or longer seldom warp in a manner which will cause trouble on the job.

This tendency of asbestos cement shingles to warp can be greatly minimized by subjecting the shingles, during the manufacturing process, preferably before coating, to autoclaving with steam at a relatively high pressure. While 3,%Z,Z87 Patented Aug. 19, 1969 such a process is efiective, it requires expensive equipment and also increases handling operations and costs.

If a simple and inexpensive means could be found to eliminate or minimize the above mentioned warping, a marked advance in the art of manufacturing asbestos cement shingles would ensue.

It is accordingly an object of this invention to provide a process for minimizing the warping of asbestos cement shingles which have been coated and subsequently baked.

Another object of this invention is to provide a bakedon coated asbestos cement shingle which is substantially Warpfree.

It is a further object of this invention to provide a substantially warp-free asbestos cement shingle having a baked-on coated embossed exterior surface.

A still further object of this invention is to provide a process for minimizing the warping of asbestos cement shingles which have an embossed surface treated with a baked-on coating by an efiicient, simple and inexpensive means.

These and other objects will be apparent by reference to the following specification and claims.

It has been found that the objects of this invention can be accomplished in an efiicient, simple and inexpensive manner by a novel treatment of the back or unexposed surface of the asbestos cement shingle, which back surface is ordinarily not coated, prior to the application and baking of a surface coating thereon in a manner which will be subsequently more clearly set forth in the following:

Accordingly in one broad form the present invention is an improved process for the production of coated asbestos shingles having a reduced warping tendency which comprises forming an asbestos cement shingle, applying a discontinuous essentially uniformly distributed water resistant coating on the back surface, predrying the back coated shingle at elevated temperatures, cooling the shingle, and applying a continuous weather resistant coating on the weather surface thereof, baking the coated shingle to cure the coating, and thereafter adjusting the moisture content of the baked shingle.

In referring to the shingles made by the process of this invention it should be understood that the exterior or front surface is referred to as the weather surface which is intended to mean the surface exposed to the weather or elements when the single is applied to a building structure in the usual manner. The rear or other major surface of the shingle is referred to as the rear, interior, other or back surface of the shingle which faces the interior of the building structure when applied in the conventional manner, and is not exposed to the elements. The length of the shingle shall also be understood to be the longest dimension, and the height as the shortest dimension, having reference in each case to the front and back of a shingle about 1 foot high and 3 feet long. The shingles are conventionally sheets about 7 thick.

In accordance with this invention, sheets or shingles are manufactured from a mixture of portland cement, asbestos fibers and finely divided silica flour, using the well known Hatschek machine, a wet method. The shingles have their surfaces embossed with closely spaced, fairly deep parallel grooves or scoring of substantially rectangular cross section. These grooves are between about to about wide, ranging in depth from 0.015 to 0.070 and are spaced fairly close together. These sheets, after curing for six to seven hours, are customarily cut into shingles such as 27 x 12 with the grooves extending parallel to the short dimension. These shingles, after further curing, are treated in the following manner. Substantially the entire back surface of each shingle is coated with a series of about A" wide parallel stripes with about a A" wide space between stripes, of a coating formula containing an aqueous acrylic emulsion which also contains shellac and a small amount of a fluorocarbon. Solid content of the back striping formula is preferably 30% to 35 Aqueous acrylic coatings, without shellac, can also be used, provided they are suiiiciently dry and hardened after the baking process so as not to cause sticking or blocking when stacked in bundles.

The shingles, after back coating, are passed through a predryer which is kept at a temperature of about 600 F. for a sufiicient time to reduce the moisture content from between about 9% and to about 2% or less. The

shingles 1 through 9. Shingles 12 through were treated with other types of materials. Shingle 16 received no back coating.

The shingles were then bundled in the regular manner and after 5 days storage they were removed from the bundle and were tested for Warping after 24 hours and 5 days. During this 24-hour and 5-day period the shingles stood on the 277 edge, free of any wrapping or other restraint. Warp is measured at the center nail hole while the shingle is standing on a 12 edge, with both 12" edges against a straight edge, such as a square.

Dried coating Warping in inches after Stripe width (in.) per 100 sq. it. removed from bundle Percent area coated area,

Shingle No. Coated Uncoated as striped (lbs) 24 hrs. 5 days 3 17 41 3 ,62 a 46.2 $4 $6 33 42 3 K32 est 50 42 0 0 V), M 66 42 0 0 M, 83 42 0 0 All 0 100 49 4 942 4 %2 3 3 50 42 4 at; 4 %g 1 50 46 e 3 :1 95 2 2 2 2 50 42 $62 3 50 21 a 4 a 1,, 50 86 4 %2 M M 50 51 4 /52 M 50 13 3 eg 50 z 0 M 50 70 %2 3 5'32 None 8 g 1 Stripes parallel to the long dimension.

2 2 squares applied as a checkerboard design.

3 Warped so that the face side is convexed.

4 Warped so that the face side is concaved.

NOTE.A11 of the shingles, with the exception of numbers 12, 13, 14 and 15, were coated with the acrylicshellac emulsion coating mentioned in the description of this invention. Shingle 12 was back coated with a 52% aqueous solution of phenol-formaldehyde; shingle number 13 with a 13.3% silicone solution; number 14 with a polyethylene emulsion of 30% and number 15*with a coating described in Patent No. 2,354,350. All percentages are the amount of solids present.

shingles are cooled and immediately thereafter the exterior surface is coated with a color composition which usually has a thermosetting plastic material, such as an acrylic, as a binder. The coated shingle is then baked by passing through a heated oven where it is subjected to hot gases of between about 285 to 455 R, which removes the water from the coating and bakes the coating as well as the back stripes. The shingles are completely bone-dry after leaving the baking oven. It is advisable to adjust their moisture content (hygroscopic moisture) to nearly that reached under ordinary job conditions which is from about 2% to 7% moisture, but ordinarily is about 4%. This is accomplished by spraying the shingles with water shortly after they leave the bake oven.

Without the use of the back treatment there would be a permanent convex bow of the face side upon the job of at least A" and quite often more, such that in applying the shingles to a flat surface they are occasionally broken or the fasteners become loosened; however, with the treatment the warp is not over about A convex or concave bow of about Ms or less is insufficient to cause difficulty upon the job. The degree of warp or curvature has reference to shingles which are up to about 3 feet in length, the most common being 24 inch or the 27%; inch shingle referred to above.

Among other factors, the degree of warp prevention is also dependent upon the percentage of the total back area covered by the coating, the amount of coating used per unit area covered and to a certain extent upon the width of the stripes, as well as the type of coating used. The accompanying table illustrates the effect of the above mentioned variables upon the prevention of warp. The shingles used to obtain the forthcoming data were from regular production, following the above procedure with the back side coated with stripes as mentioned in the table. In the case of shingles 1 through 9 which were made to determine the effect of the percentage of area covered and also the width of the stripes, an attempt was made to keep the weight per square foot of the coating the same. Shingles 10 and 11 were treated to show the effect of lesser and greater amounts of coating than that used in From the above data, it is evident that a wide range of percentages of coated areas can be followed and still effect a marked decrease in warping. Note that a complete back coverage is not effective, being as bad if not worse in warping than no treatment at all. However, as much as an 83% coverage is effective, through it is desirable that at least about 15% of the back area should be exposed. A coverage of only 33% was not as effective as a 50% coverage, which is very effective. About a 44% coverage has been used in commercial production with good results. However, not less than about a 15 nor more than about 85% coverage of the back area should 'be used, and preferably between about 40% and 75%. Note that in the range of from 50% to 83% coverage, a coating weight amounting to .42 lb. per sq. ft. is quite efiective, while .21 lb per 100 sq, ft., shingle 10, is less effective, and .86 1b., shingle 11, is very effective, but apparently not much better than when .42 lb. per 100 sq. ft. is used. In the case of the acrylic-shellac coating it is understood that at least about .3 lb. solids per 100 sq. ft. coated area is required, but note that only .13 lb. per 100 sq. ft. of the silicone back coating markedly reduced the warping. All coating weights are given on a solids basis.

It is not desirable to apply too thick a back striping as such may run down and form hard beads when the shingles are placed in a vertical position during processing. These beads may be pressed into the face of the adjacent shingle in the bundle, and cause undesirable surface marking. Excessive back striping may bubble when subjected to heat, and also cause surface blemishes in the bundle. Care must also be followed in preventing the back coating from covering a portion of the face surface as it may prevent proper adhesion of the surface coating to the shingle. Note also that the wide three inch alternate coated and uncoated stripes are not quite as effective as the narrower; hence, wide stripes are less preferred. A coating applied in a checkerboard design or in stripes parallel to the longer side of the shingle is also less preferred.

Other water resistant coatings can be used besides the above identified acrylic-shellac formula, such as water dispersed phenol formaldehyde, which is subsequently hardened during the baking operation, shingle 12; silicone, shingle 13; and polyethylene, shingle 14. An alkali metal silicate coating such as described in Patent No. 2,354,350 has also been found to have some value, see shinkle 15. While the foregoing examples are directed to a number of specific coating materials which have been found useful in practicing the present invention, it should be understood that they were merely exemplary and that a wide variety of water resistant coatings may be so employed with the same beneficial effects. It should also be understood, of course, that the usual plasticizers, accelerators, coagulants, surfactants, etc., which will render a particular coating material more effective as such, are

intended to be incorporated in the description of this in vention. These conventional additives are too numerous to mention for the wide range of water resistant materials which can be used to form the coating, but are known to those skilled in the art.

Some of the other materials, such as the phenol formaldehyde, the silicone and the polyethylene, impart some color to the coating. This has been found to be undesirable, as in the field the tradesmen mark the back of the shingle for cutting and any substantial coloring may obscure such marking. In addition, a dark back striping material on the shingle edges is more difficult to hide and cover with a White or light colored face coating. The preferred amount of the coating to be used is dependent upon the type and can be determined by empirical methods by those skilled in the art following the above set forth description of the invention. At least about .1 lb. per 100 sq. ft. of the coated area should be used.

It is preferred to have the stripes extend in the short direction of the shingle, for not only does this simplify the application thereof but it also is more effective than those parallel to the long dimension. It is also preferred that the coating stripes be continuous rather than broken. Roller coating of the back surface is a convenient technique which lends itself to continuous production methods.

While the advantage of this invention is most noticeable in preventing the warping of a baked-on surface coated shingle with embossed deep textures, which is the most likely to severly warp, it also is effective in the prevention of the warping of shingles having a baked-on coated surface without an embossed surface.

By following this invention it is not necessary to use the expensive autoclaving procedure as it has been found that when the shingles have been treated in the manner forming the subject of this invention, complaints due to warping have been substantially eliminated without resorting to such autoclaving.

The exact reason why such a limited treatment of the back of an asbestos cement shingle will prevent or decrease warping is not clear. A theory is that the coating seals the asbestos cement shingle sufficiently in the back to compensate for the sealing tendency of the baked-on coating on the surface. Thus, any remaining water in the shingle will tend to be driven out equally from both sides of the shingle, whereas if the water comes off from one side only or in greater amounts, that side will become shorter in length and lead to warping. It is known that the back coating should be applied before the predryer. It is also known that it is not necessary that the back coating form a film upon the surface, for it can penetrate into the surface of the shingle, leaving very little exposed. It is important, however, that the back coating be water resistant and more impermeable to the passage of water and water vapor than the plain shingle surface.

While several particular embodiments of this invention are shown above, it will be understood, of course, that the invention is not to be limited thereto, since many modifications may be made, and it is contemplated, therefore, by the appended claims, to cover any such modifications as fall within the true spirit and scope of this invention.

I claim:

1. In a process for the production of a coated asbestos cement shingle having a reduced warping tendency including the steps of forming an asbestos cement shingle which in use has a normally exposed weather surface and a normally unexposed back surface, predrying the shingle at elevated temperatures, cooling the shingle, applying a continuous weather resistant coating on the weather surface of the shingle, baking the coated shingle and adjusting the moisture content of the baked shingle, the improvement which comprises applying a discontinuous coating relatively impermeable to water vapor in a predetermined pattern distributed over the entire back surface of said shingle prior to the predrying step wherein the percentage of coated surface provided by the discontinuous coating ranges from 15 to 85% thereof.

2. A process according to claim 1 wherein the discontinuous coating is a plurality of parallel spaced stripes.

3. A process according to claim 1 wherein the percentage of coated surface provided by the discontinuous coating applied to the back surface of the shingle ranges from 40% to thereof.

4. A process according to claim 1 wherein said shingle has a short and a long surface dimension and the weather surface of said shingle is embossed with a plurality of grooves running generally parallel to the shorter dimension of the weather surface.

5. A process according to claim 1 wherein the discontinuous coating is essentially colorless.

6. A process according to claim 1 wherein said shingle has a short and a long surface dimension and the weather surface of said shingle is formed with a plurality of grooves running generally parallel to the shorter dimension of the weather surface and wherein the discontinuous coating applied to the back surface is a plurality of spaced stripes running in the same direction as the grooves.

7. A process according to claim 2, wherein said shingle has a short and a long surface dimension and the stripes run parallel to the shorter dimension of the surface of said shingle.

8. A process according to claim 6 wherein the percentage of coated surface provided by the discontinuous coating applied to the back surface of the shingle ranges from 40% to 75% thereof.

9. A warp resistant coated asbestos cement shingle prepared in accordance with the process of claim 1.

References Cited UNITED STATES PATENTS 2,044,782 6/1936 Harshberger 52-419 X 2,863,405 12/1958 Liebrook et al. 52-420 X 2,935,416 5/1960 Dunbar et al 117-43 X 3,085,907 4/ 1963 Zdanowski et al. 3,106,486 10/1963 Harren et a1 117-123 3,197,331 7/1965 Rohn 117-123 3,247,631 4/1966 Lovness 52-420 X ALFRED L. LEAVITT, Primary Examiner ALAN GRIMALDI, Assistant Examiner US. Cl. X.R. 

